I've just found myself in the same position. I'm digging into possible issues.

UPDATE:

After trying 573 different solutions, the ultimate solution seems to have been to simply uninstall the driver manually from Windows device manager, without deleting the driver, then refreshing to let Windows reinstall it manually.

After that, FreeSync started working again.

Along the chain of events I discovered a few weird configuration issues:

My monitors both were running at 59Hz (changed to 60Hz) and my main monitor (AOC FreeSync 144Hz 2460G4) had reverted to the generic monitor driver.

I resolved those issues prior to trying the manual forced reinstall of the core driver, so you may want to go that route as well.